Mike Kirda,
Thanks for your offer to help trim this young man's Science Olympiad model! I have told Jack and his mother about it, and they are considering coming to the next Bong Eagles indoor event Wednesday, February 1st. I am pretty sure it would be Jack and his mother, rather than Jack and I who would visit. Is that when you meant you could help him trim it? It's a challenge, because the drive is more than two hours each way, and it's a school night.
Jack is in Middle School. He has built a model from a kit. I didn't ask what the model is called or who makes the kit. Jack constructed it quite well, using Duco cement. The model is supposed to be capable of flights longer than four minutes. It is just over the minimum weight, and required a bit of clay to reach that weight, and is near the maximum size for wing span, chord, and stabilizer span. The wing is on a sliding mount. It has an Ikara prop, cut down to the diameter limit. The CG is a little forward of the trailing edge, the plan shows it a little aft of it. He says it stalls if he moves the CG back. There is a large wing twist, left inner panel leading edge twisting downward quite a bit by the polyhedral joint. The rear of the rudder is offset to the right about 1/8 inch or more. The prop bearing presses into a snug mount with no provision for adjustment. There is a little right thrust, but I think it's less than the recommended three degrees, with no up or down thrust. The pylon is a little to the right of the wing's center. The wing is mounted offset to point a little to the left (leading edge pylon connection more to the right than the trailing edge.)
His best flight so far has been about 80 seconds, and lands with about 150 turns left in the motor. This is in a gym with about an 8 meter ceiling, with about 1,350 turns on a 0.058 inch one and a half gram motor. Jack says the motor could be wound as high as about 1,950 turns, so he is a long way from using its full power. The model may be flying nearly as long as it could under these conditions. The usual pattern is a tightening turn to the right after launch, diminishing to about an eight foot diameter circle near the end of the flight. The video he showed me of another model showed it flew in left circles of quite constant size. Jack says his model climbs steeper initially than the one in the video. I hope to see a practice session in the gym this week. That may be Jack's only chance to fly again before the first round of competition. He says there are four others in his school doing the Wright Stuff event, but no guidance from his teachers.
I think the model is designed to turn left, and the right rudder is forcing it the other way. I think it needs less twist in the wing, the front pylon adjusted a little lower and the CG moved back, and the rudder adjusted closer to straight. Then it should turn left for the entire flight. Does any of this sound about right? Does any of it fly in the face of how you adjust your models?
I have recommended Jack joins this group. I hope he does. I know you would welcome him, and be able to provide better advice than I can!
Don Weigt
Received on Mon Jan 16 2017 - 07:55:37 CET
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